docs: update build performance benchmarks (v2.4.0)

[github-actions]

Automated build benchmark update for v2.4.0 from workflow run #65.

[greptile-apps]

Greptile Summary

Automated benchmark update for v2.4.0 from CI workflow run; all metrics are internally consistent between README.md and generated/BUILD-BENCHMARKS.md.

Key observations:

• File count increased from 109 to 115 files (+6 files)
• Native build speed: 2.1 → 4.7 ms/file (↑147% regression)
• WASM build speed: 6.4 → 9.4 ms/file (↑42% regression)
• Added native engine metrics for incremental rebuilds and query latency
• Estimated 50k file build time increased from ~105s to ~235s

Note: The performance regressions (147% native, 42% WASM) are disproportionate to the 5.5% file count increase, which may warrant investigation of whether new files are particularly complex or if there's an underlying performance issue in the codebase.

Confidence Score: 5/5

• This PR is safe to merge - automated documentation update with no code changes
• Documentation-only PR with properly formatted benchmark data that is internally consistent across both files; no syntax errors or logical issues detected
• No files require special attention - both files are auto-generated and properly formatted

Important Files Changed

Filename	Overview
README.md	Updated performance metrics table with v2.4.0 benchmarks; numbers consistent with detailed report
generated/BUILD-BENCHMARKS.md	Added v2.4.0 benchmark data with native engine metrics; all values properly formatted and internally consistent

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